Olefin polymers such as, for example, polyethylenes, are very important chemicals. For many applications of these polymers, toughness, strength, and environmental stress cracking resistance are important properties. Generally, these properties can be improved by increasing the molecular weight of the polymers. However, as the molecular weight of the polymers increases, the processability such as, for example, extrusion, molding, thermoforming, and rotational molding of the polymers decreases.
It is known that, the processability of the polymers can be improved by providing the polymers with a broad, bimodal, or multimodal molecular weight distribution in which the properties described above are attained and, in the mean time, the processability of the polymers is also improved. For example, olefin polymers having a multimodal molecular weight distribution process more easily, i.e., they can be processed at a faster throughput rate with lower energy requirement. Such polymers have reduced melt flow perturbations and are preferred due to improved properties for applications such as high strength films.
There are many known processes for producing olefin polymers having multimodal molecular weight distribution. However, each process has its own disadvantages; for example, an olefin polymer having a multimodal molecular weight distribution can be made by employing two distinct and separate catalysts in a polymerization reactor wherein each catalyst produces a polymer having a different molecular weight distribution. The catalyst feed rate is generally hard to control and the polymer particles produced are not uniform in size. Furthermore, segregation of polymer particles during storage and transfer of polymer can occur thereby producing non-homogeneous products.
An olefin polymer having a multimodal molecular weight distribution can also be produced by a sequential polymerization in two separate reactors or by blending polymers of different molecular weight distribution during processing of polymers. However, both of these methods increase capital and manufacturing costs.
Therefore, there is an ever-increasing need for developing an improved process for an improved catalyst composition which can be used to produce an olefin polymer having a multimodal molecular weight distribution. It would also be a great contribution to the art if an improved catalyst and an olefin polymer produced therefrom were provided.